Material opacity not working
What render engine are you using? Are you rendering on the GPU?
If you are using EEVEE, check the blend method of the material: https://docs.blender.org/manual/en/latest/render/eevee/materials/settings.html#blend-mode
If you are using Cycles and are rendering on the GPU, try rendering on the CPU. It may be a GPU driver problem.
If the problem still persists, call your mom. :-)